P03B9
Cylinder 4 Pressure Too High
Generic OBD-II
Real-world scan data
Seen in
21
scans in the past year
Found in
<0.1%
of scans
<0.1%
of scans that found faults
Figures reflect only diagnostic scans recorded through our own apps and tools. Cars are typically scanned because a symptom or warning light prompted it, so these counts describe our scan records — not the incidence of faults in any model, and not the quality, reliability, or safety of any vehicle. No comparison between manufacturers or models is implied. All trademarks belong to their respective owners; no affiliation or endorsement is implied.
Common symptoms
What you'll notice
- Check for a faulty spark plug or ignition coil and replace if necessary.
- Inspect the fuel injector for any clogs or leaks and clean or replace if needed.
- Verify the engine timing and adjust if it is off.
- Check the engine's air intake system for any restrictions or blockages and clean or repair as required.
- Conduct a compression test on cylinder 4 to identify any potential issues with the piston rings or valves, and repair accordingly.
Common causes
Most likely first
- Faulty fuel injector in cylinder 4
- Malfunctioning spark plug in cylinder 4
- Engine overheating leading to high pressure in cylinder 4
- Issues with the engine control unit (ECU) causing incorrect fuel mixture in cylinder 4
- Compression leak in cylinder 4
How to diagnose & fix
Work through it in order
- Engine misfire or rough idling
- Decreased engine power
- Engine stalling or hesitation
- Loud knocking or pinging sounds from the engine
- Increased fuel consumption
Read & clear P03B9 yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.